1. Field of the Invention
The present invention relates to a lens such as a spectacle lens, a camera lens or a magnifying lens with a surface layer that displays excellent stain resistance and excellent wipeability of stains such as hand grime and fingerprints.
2. Description of the Prior Art
Lenses, and particularly those lenses that are frequently handled, are prone to stain adhesion arising from hand grime, fingerprints, skin oils, sweat, saliva, and cosmetics such as hair setting products and the like, and the complete removal of such stains by careful wiping takes considerable time.
Furthermore, an anti-reflective film is typically provided on the surface of spectacle lenses and camera lenses, and this anti-reflective film is also prone to stain adhesion arising from hand grime, fingerprints, skin oils, sweat, saliva, and cosmetics such as hair setting products and the like. Moreover, adhesion of these types of stains can alter the surface reflectance, meaning the stains are more conspicuous than those on a simple transparent plate, and removal of the stains by wiping is also difficult. A solution to these problems has been keenly sought.
Conventional examples of optical products such as lenses with anti-reflective properties that offer improved contamination resistance include products comprising a substrate on which is formed an anti-reflective layer formed from either a single layer, or a plurality of layers, of an inorganic material comprising silicon dioxide as a primary component, formed by a PVD (Physical Vapor Deposition) method such as vacuum deposition, ion plating or sputtering, in which a cured layer of an organic polysiloxane-based polymer or a polymer containing perfluoroalkyl groups is provided on the surface of the anti-reflective layer (Japanese Post-Examination Patent publication (kokoku) No. 6-5324(JP6-5324B)). However, if contamination such as hand grime or fingerprints adhere to this type of cured layer, removal of the contamination by wiping with tissue paper or the like is difficult, and the wiping action tends to simply spread the contamination out in a thin film. In addition, over vigorous rubbing can cause scratching of the anti-reflective film, meaning contaminants cannot be satisfactorily wiped off.
Furthermore, compounds containing perfluoropolyether groups typically have extremely small surface energies, and consequently display good water and oil repellency, chemical resistance, lubrication, mold releasing properties, and stain resistance. These properties are widely utilized industrially in products such as water and oil repellent stain prevention agents for paper and fiber, lubricants for magnetic recording media, oil retaining agents for high precision equipment, mold releasing agents, cosmetics, and protective films and the like. However, the properties described above mean that the compounds also display very poor adhesion and bonding to other materials, and conventional perfluoropolyether group containing compounds, even if they are able to be applied to a substrate surface, are unable to form films or bind strongly.
On the other hand, the use of silane coupling agents to achieve bonding between the surface of a substrate such as glass or cloth and an organic compound, is well known. Silane coupling agents comprise an organic functional group and a reactive silyl group (usually an alkoxysilyl group) within a single molecule. For example, silane coupling agents containing alkoxysilyl groups form polysiloxane structures that function as covering films by undergoing a hydrolysis reaction and a condensation reaction with moisture in the air. At the same time, the aforementioned organic functional groups, together with the aforementioned reactive silyl groups, bond chemically and physically to the surface of the substrate such as glass or metal, forming a strong film that displays good durability. Utilizing these properties, silane coupling agents are widely used in surface coating agents for a variety of substrates.
An example of a surface treatment agent that combines the characteristics of the aforementioned perfluoropolyether group containing compounds and silane coupling agents, thereby providing a surface treatment agent that forms a strongly bonded film on a substrate surface, and also displays superior water and oil repellency, stain resistance, chemical resistance, lubrication, and mold releasing properties has been reported in Japanese Laid-open publication (kokai) No. 9-258003 (JP9-258003A), which discloses a lens with a stain resistant layer that utilizes a fluorine containing silane compound represented by a formula (2) shown below: (wherein, Rf is a straight chain or branched chain perfluoroalkyl group of 1 to 16 carbon atoms, X is an iodine atom or a hydrogen atom, Y is a hydrogen atom or a lower alkyl group, Z is a fluorine atom or a trifluoromethyl group, R1 is a hydrolysable group, R2 is a hydrogen atom or an inactive monovalent organic group, c, d, e and f are each integers from 0 to 200, g is either 0 or 1, p and q are each integers from 0 to 2, and k is an integer from 1 to 10).
However, although fluorine containing silane compounds represented by the above formula (2) contain a comparatively large proportion of hydrolysable groups within each molecule, these hydrolysable groups exist only at one terminal of the molecular chain, and consequently the adhesion of these compounds to substrates is not entirely satisfactory, leading to durability problems, and when the compounds are used as surface treatment agents for lenses, the desired properties cannot be maintained over long periods, making them not particularly suitable.
(Patent applications for inventions pertaining to anti-reflective filters using the perfluoropolyether modified silane disclosed in a first aspect of the present invention have already been submitted by the applicant of the present invention, in Japanese Patent application No. 2001-310247 and Japanese Patent application No. 2001-378382.